低透气性煤孔隙结构连通率对煤层渗透性的影响规律研究

Research on influence of pore structure connectivity of low gas permeability on coal seam permeability

为研究低透气性煤的孔隙结构特征及孔隙连通程度,对原煤煤样进行试验,分析饱和水和残余水状态下煤样的T2曲线,得到煤样的自由流体值、束缚流体值、有效孔隙率、孔径分布及渗透率等参数,建立了孔隙连通率定量计算模型。结果表明:煤样孔隙率为6.30%~11.02%,孔径分布呈3段式,孔隙主要集中分布在0~100 nm段,微小孔发育、中大孔及裂隙不发育;吸附孔与孔隙率成反比,渗流孔与孔隙率成正比;煤样孔隙连通率为31.50%~62.05%,孔隙连通率受孔隙尺度的影响,煤样孔径在100 nm以下的孔隙连通率最高为58.45%,孔径为100 nm以上的孔隙连通率在94%以上;孔隙连通率与孔隙率、有效孔隙度、渗透率表现出了较好的正相关关系。

In order to study the pore structure characteristics and pore connectivity of low-permeability coal,low-field nuclear magnetic resonance technology was used to analyze the raw coal sample.The T2 curve of the coal sample under saturated water and residual water conditions was used to obtain the free fluid value,irreducible fluid value,effective porosity,pore size distribution,and permeability etc.A quantitative calculation model of pore connectivity was established on the basis of these works.The results showed that the porosity of the experimental coal sample was changing from 6.30%to 11.02%,and the pore size was distributed in three stages,the pore size was mainly concentrated in the 0 nm to 100 nm segment.The fissures and the pores which including macropore and medium ones were not developed.Adsorption pore was inversely proportional to porosity.Percolation pore was proportional to porosity.The pore connectivity of experimental coal sample was varying between 31.50%and62.05%.The pore connectivity was affected by the pore size,and the pore connectivity rate of the experimental coal sample with a pore size below 100 nm was up to 58.45%.The connectivity rate of pores with pore size over 100 nm was above 94%.Pore connectivity has a good positive correlation with porosity,effective porosity,and permeability.